The present invention relates to a novel low-resistance interconnector and a method for the preparation thereof. More particularly, the invention relates to a low-resistance interconnector used for electrically connecting oppositely facing electrodes in arrays on two different electronic devices as in the electric connection between a glass substrate plate and a printed circuit board of a liquid-crystal display device, between two electronic circuit boards and between an IC chip and an inspection instrument thereof as well as to an improved method for the preparation thereof.
As is known, several types of interconnectors are currently used with the above mentioned object to establish electric connection between two arrays of electrode terminals on two electronic unit devices. One of the most important classes of interconnectors include those belonging to the so-called zebra type interconnectors, in which the principal part is an integral elongated piece consisting of an alternate stratification of layers of an electroconductive rubber and layers of electrically insulating rubber stacked one on the other in the lengthwise direction as is disclosed in Japanese Patent Kokai 50-94495. Most conventional interconnectors of the other class are those belonging to the class of the so-called anisotropically electroconductive interconnectors consisting of a sheet of an insulating rubber as the matrix and a multiplicity of very fine metal filaments embedded in the matrix as aligned to run in the direction, typically, perpendicular to the surface of the sheet as is disclosed in Japanese Patent Kokai 53-5147991.
These conventional interconnectors have their own advantages and disadvantages. For example, a zebra-type interconnector has a problem that, since the integral elongated piece consisting of an alternation of conductive and insulating rubber layers is prepared by slicing an alternately laminated block of these two different layers into sheets followed by chopping of the sliced sheets into elongated pieces, occurrence of a "skew" in slicing and chopping is more or less unavoidable resulting in a decrease in the dimensional accuracy of the interconnector so that the interconnector is not suitable for use in the electric connection of electrode arrays in a very fine pitch of the electrode arrangement. In addition, the volume resistivity of the electroconductive rubber layers cannot be low enough so that the electric resistance between two electrode terminals connected therewith is necessarily high and cannot be uniform and the electric current passing through the layer of the conductive rubber is limited, for example, not to exceed 10 mA since a larger current necessarily results an undue temperature increase in the interconnector to decrease the stability of electric connection with the interconnector. When IC chips and similar chips having a great number of electrode terminals in an electrode array are to be electrically connected with an interconnector, moreover, uniformity and reliability of electric connection can be ensured only by increasing the contacting pressure between the interconnector and the electrode arrays so that the overall load on the electrode terminals of the IC chip or on the inspection instrument is necessarily increased.
An anisotropically electroconductive interconnector, on the other hand, has different problems and disadvantages. For example, the fine metal filaments embedded in the rubbery matrix are liable to cause buckling by repeating bending and stretching so that the interconnector is not suitable, for example, in an inspection instrument for IC chips in which one and the same interconnector is used repeatedly for a large number of IC chips. Reliability of electric contacting between the end points of all of the fine metal filaments and the electrode terminals can be ensured only by increasing the contacting pressure between the interconnector and the electrode terminals resulting in overloading on the electrode terminals of the IC chip or on the inspection instrument. The end points of the fine metal filaments usually have no flat and uniform surface so that the fine metal filaments and the electrode terminal are connected only by point-contacting sometimes resulting in an incomplete electric connection. In addition, it is sometimes necessary to provide a plating layer of gold on the end point surface or over the whole surface of each of the fine metal filaments in order to decrease the contact resistance between the metal filaments and the electrode terminals or to ensure stability in the embedded condition of the metal filaments in the rubbery matrix.
Although conventional zebra-type interconnectors can be used for the electric connection of a semiconductor device having a high input impedance such as field-effect transistors and similar transistors where the continuity current is consequently small with a negligibly small voltage drop and heat generation even when the internal resistance of the interconnector is relatively large, they cannot be used when a low internal resistance of the interconnector is essential as in the electric connection of a color liquid-crystal module and a black-and-white liquid-crystal module of 16 gradations or more, when it is desired to have the resistance values of the electroconductive layers as uniform as possible or when a relatively large electric current is to be passed through the interconnector as in the plasma display modules and in the electric connection of a power circuit and similar power circuits.